The present invention relates to a hydraulic actuating system comprising a pump which, in operation, continuously supplies fluid out of a reservoir into a pressure line, in combination with a pressure-limiting valve recirculating flow to limit the pressure in the pressure line, with a control valve connected to the pressure line, and with an expansible chamber actuating device such as an operating cylinder which is connectable to the pressure line via the control valve.
Actuating systems of this type are commonly known, see e.g. the journal `Konstruktion 12` (1960), volume 9, page 380, pictures 13 and 17, and are typically of simple construction. A disadvantage of these actuating systems is that, in order to attain high speed operation of the operating cylinder, pumps with a correspondingly great displacement volume are required. However, such large pumps must be of increased design strength and require increased space. Large displacement pumps increase the energy demand, which has to be considered as loss in the periods of operation in which the control valve is closed and the delivery flow of the pump is discharged through the pressure-limiting valve such that no work output is realized.
Hydraulic actuating systems are further known (see German published patent application 23 24 059, as an example) wherein the pump charges a pressure accumulator from which hydraulic fluid flows for use by the operating cylinder. These systems are comparatively sophisticated because they necessitate a pressure accumulator with a gas chamber separated by a diaphragm or a piston, and usually also an accumulator-charging valve.
It is the object of the present invention to enable an increase in the speed of operating of the operating cylinder in a hydraulic actuating system of the above type beyond the extent predetermined by the fluid delivery rate of the pump without the employment of conventional pressure accumulators.